El Niņo's impact may extend to the shores
of East Africa

People living along the Pacific coast have
learned to respect the awesome power of El Niņo
­ the periodic warming and cooling of the
Pacific Ocean that can bring torrential rainfall
or extreme drought every three to seven years.

Now researchers analyzing coral samples
drilled off the African coast have discovered
that El Niņo's influence may stretch well beyond
the Pacific into the waters of the Indian Ocean.

Robert B. Dunbar, Stanford professor of
geological and environmental sciences, and
University of Arizona professor of geosciences
Julia E. Cole describe their findings in the Jan.
28 issue of the journal Science.

Using underwater drills, Dunbar's team removed
12-foot-long core samples from a living colony of
coral growing in the waters of Kenya's Malindi
Marine Park (see photo 1).

Like trees, coral skeletons form annual growth
rings that accumulate over hundreds of years. The
Malindi core samples provide a 194-year record of
growth dating back to 1801 (see photo 2).

As they grow, coral skeletons take up a
mixture of different types of the chemical
element oxygen. One type is heavier than the
other, and as the coral experiences seasonal and
long-term changes in water temperature, the
relative proportion of heavy and light oxygen in
the skeleton also changes.

By measuring how much heavy oxygen is present
in each growth ring, scientists can determine
past changes in water temperature.

When Dunbar and Cole analyzed the quantity of
heavy oxygen in the Malindi samples, they made a
remarkable discovery: Surface temperatures in the
western Indian Ocean have risen and fallen
roughly every 10 years in a pattern almost
identical to the periodic warming and cooling
that occurred in the tropical Pacific.

"It brings home the message that the
Pacific Ocean exerts a tremendous impact on the
global climate," Dunbar says. "This is
strong evidence of a big influence from the
Pacific on a decadal time scale."

The Malindi corals also revealed that the
surface temperature of the Indian Ocean has risen
approximately 2.3 degrees F (1.3 C) since 1801.

"This is a big increase," Dunbar
says, noting that the largest rise occurred in
the late 20th century ­ possibly the result of
an artificial greenhouse effect caused by people
burning gasoline and other fossil fuels.

Dunbar and his colleagues plan to continue
their research to determine if El Niņo has any
effect on the severity of monsoon rainfall along
the Indian Ocean coastline. Eventually scientists
may be able to predict severe monsoon seasons
months in advance, a breakthrough that could
benefit millions of coastal residents who face
severe flooding in Kenya, India and nearby
countries.

Two other researchers co-authored the Science
article: Timothy R. McClanahan of the Wildlife
Conservation Society and Nyawira A. Muthiga of
the Kenya Wildlife Service.